The invention relates to a delivery for a sheet-processing machine, especially a printing machine, including a sheet brake for braking processed sheets from a processing speed to an output speed, a sheet conveyor for transporting the processed sheets in a conveying direction at the processing speed and for transferring the processed sheets to the sheet brake, and structure forming a gap which, during operation, is connected to a vacuum generator and over which the sheet conveyor pulls the sheets for smoothing them before they are transferred to the sheet brake, and also to a sheet-processing machine, especially a printing machine, equipped with the delivery.
A delivery of the foregoing type is disclosed in published Swiss Patent Document CH 611 579 A5 which describes a subassembly by which, directly after the processed sheets have been smoothed out, the sheets are braked. This subassembly is formed with two gaps following one another in the processing direction and, during operation, connected to a vacuum generator. A sheet conveyor having grippers which grip a respectively leading edge of the sheets guides the sheets over the two gaps. In order to smooth the sheets out, provision is made for them to be pulled into that gap which is upline of the other of the two gaps, under the action of the vacuum generator, as the sheets sweep over the subassembly, while a respective leading edge of the sheets is positively guided by the grippers. The positive guidance of a respective one of the sheets is discontinued when the sheet leaves the upline gap but still covers the downline gap of the two gaps. With this deliberate discontinuance or cancellation of the positive guidance of the respective sheet, provision is made for braking the latter under the action of the vacuum generator by sucking the sheet against the edges of the downline gap.
This braking process is difficult to control, however, particularly inasmuch as when the respective sheet exposes the upline gap, the pressure relationships in this gap and in the downline gap are changed abruptly.
It is accordingly an object of the invention to provide a delivery of a sheet-processing machine of the foregoing general type with a subassembly which permits the smoothing and subsequent braking of a respective sheet and which, when the braking process is started, does not cause any change in the pressure relationships created by the vacuum generator. With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a delivery for a sheet-processing machine, comprising a sheet brake for braking processed sheets from a processing speed to an output speed, a sheet conveyor for transporting the processed sheets in a conveying direction at the processing speed and for transferring the processed sheets to the sheet brake, and a body defining a gap which, during operation, is connected to a vacuum generator and over which the sheets are pullable by the sheet conveyor for smoothing the sheets before they are transferred to the sheet brake, the gap being formed at the sheet brake.
In accordance with another feature of the invention, the sheet brake includes a rotating body having a cylindrical outer face which, during operation, rotates positively at a peripheral speed lower than the processing speed, forms with the outer face thereof a first edge of the gap, which is at a downline location with respect to the conveying direction, and pulls a respective sheet, which is transferred to the sheet brake and braked, over the gap in the conveying direction.
In accordance with a further feature of the invention, a second edge defining the gap is formed on a component that is stationary during operation, the second edge being upline from the first edge with respect to the conveying direction.
In accordance with an added feature of the invention, the delivery includes a further cylindrical rotating body which, with a cylindrical outer face thereof, forms a second edge of the gap, the second edge being disposed upline from the first edge with respect to the conveying direction, the two rotating bodies having identical rotational movements during operation.
In accordance with an additional feature of the invention, the cylindrical rotating body forming the first edge is formed as a hollow body with an outer jacket having apertures formed therein and communicating with the interior of the hollow body.
In accordance with another aspect of the invention, there is provided a sheet-processing machine, including a delivery, comprising a sheet brake for braking processed sheets from a processing speed to an output speed, a sheet conveyor for transporting the processed sheets in a conveying direction at the processing speed and for transferring the processed sheets to the sheet brake, and a body defining a gap which, during operation, is connected to a vacuum generator and over which the sheets are pullable by the sheet conveyor for smoothing the sheets before they are transferred to the sheet brake, the gap being formed at the sheet brake.
In accordance with a concomitant aspect of the invention, there is provided a printing machine, including a delivery, comprising a sheet brake for braking processed sheets from a processing speed to an output speed, a sheet conveyor for transporting the processed sheets in a conveying direction at the processing speed and for transferring the processed sheets to the sheet brake, and a body defining a gap which, during operation, is connected to a vacuum generator and over which the sheets are pullable by the sheet conveyor for smoothing the sheets before they are transferred to the sheet brake, the gap being formed at the sheet brake.
Thus, in order to achieve the objective of the invention, the gap provided in the delivery described in the introduction hereto for smoothing a respective sheet is formed at the sheet brake. To this extent, this gap is given a dual function, because, under the action of the vacuum generator, it smoothes the respective sheet positively guided by the sheet conveyor by pulling the sheet into the gap and, after the sheet has been released by the sheet conveyor, the gap continues to remain as a vacuum chamber that is covered by the respective sheet, with the effect that the released sheet is pressed against the edges defining the gap by a vacuum prevailing in the gap and, in the process, is braked.
Furthermore, this dual function also leads to this extent to a simpler construction of the subassembly serving to smooth and brake the sheets, than that required by just a single gap for smoothing and braking.
According to a development, provision is made for the sheet brake to comprise a rotating body having a cylindrical outer face which, during operation, rotates positively at a peripheral speed lower than the processing speed, forms with the outer face a first edge of the gap, which is downline with respect to the conveying direction, and pulls a respective sheet, which is transferred to the sheet brake and braked, over the gap in the conveying direction.
Assurance is therefore provided that a respective sheet is not braked to a standstill before it has left the sheet brake.
The reason for this is that, in the aforementioned development, the rotating body forming the first edge of the gap exerts a forward drive force directed in the processing direction on the braked sheet, in spite of the braking action of the sheet brake.
Although, in the aforementioned development, the sheet brake has a braking element in the form of the rotating body forming the first edge, it has a greater braking action than a conventional sheet brake, disclosed for example by the published German Patent Document DE 196 16 423 C2, having a braking element formed as a rotating body, in the outer cylindrical face of which there terminate suction openings which, during operation, successively communicate with a vacuum generator and through which, in particular in the case of relatively stiff sheets, a given amount of unwanted air flows. The aforementioned greater braking action in the case of the subject of the invention results from a relatively large area, necessitated by the gap, which is covered by the sheet and is under a vacuum.
According to a first refinement of this development, a second edge of the gap, which is upline from the first edge, is formed on a component that is stationary during operation. overall, this therefore results in an extremely simple subassembly for smoothing and braking the sheets.
Another refinement of the development is distinguished by a further cylindrical rotating body which, with the outer face thereof, forms a second edge of the gap, which is upline from the first edge with respect to the conveying direction, and the two rotational bodies have identical rotational movements during operation.
In this case, the further rotating body also exerts a forward drive force on a respectively braked sheet. This ensures that the respective sheet, after the latter has been braked, still experiences a forward drive force on the part of the sheet brake, even under such frictional relationships at the contact points between the edges of the gap and the sheet wherein a frictional force acting upon the sheet from the second edge of the gap exceeds the forward drive force which the sheet experiences from the rotating body forming the first edge.
In a further refinement of the development, the rotating body forming the first edge is formed as a hollow body with an outer surface which has apertures formed therein and communicating with the interior of the hollow body.
To this extent, this refinement provides a further reinforcement of the braking action, because a respective sheet makes contact with the rotating body forming the first edge along a relatively large wrap angle, and therefore brings about an enlargement of the perpendicular force which acts between the sheet and the rotating body.
Furthermore, a subassembly constructed in accordance with the invention for smoothing and braking a respective sheet requires a relatively small installation space, it needs only a single vacuum generator and makes it possible to dispense with additional measures which are necessary, for example, in the case of the sheet brake disclosed by the aforementioned published German Patent Document DE 196 16 423 C2, to produce the first contact between a respective sheet and the braking element. Instead, it is sufficient to bring about contact between the sheet and the edges of the gap which is necessary for smoothing the sheet. However, this can be implemented by a single blast or blown-air curtain directed onto the upper side of a respective sheet in the vicinity of the gap.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a delivery for a sheet-processing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: